On medium heat, add butter, chicken, celery, onion, green onion, italian parsley, salt, pepper and garlic powder to a large pot or dutch oven. Cook for 10-15 minutes.
Add chicken stock and bay leaves and bring to a boil. Boil for 15 minutes or until celery is tender.
Reduce heat to medium low and remove bay leaves. Add cream, water and whole milk and stir until well blended.
Add orzo and stir every few minutes until soup is thick and creamy, 30-45 minutes.
Whenever a soup calls for chicken, I always use a roasted chicken. It adds a richness to soup that you can't get with plain chicken breasts. You can get them at any grocery store in their deli section, and Costco sells a huge roasted chicken for $5.00. If you don't use the whole thing, freeze the rest!